Device for absorbing electromagnetic radiation

ABSTRACT

The invention relates to a device ( 3 ) for absorbing electromagnetic radiation, in particular solar radiation. The device ( 3 ) has at least one 11cxible film pocket ( 4 ) that is divided into chambers ( 15 ). Said chambers ( 15 ) are connected to at least one feed clement ( 5 ) and at least one discharge element ( 6 ), by means of which a heat transfer medium can be fed to and discharged from the chambers ( 15 ). To prevent a build-up of pressure in the heat transfer medium caused by gravity and thus unwanted stress on the film material, at least one pressure reducing clement ( 21 ) is provided between at least two of the chambers ( 15 ) or fllm pockets ( 4 ). Said pressure reducing clement ( 21 ) limits the pressure of the heat transfer medium.

The invention relates to a device for absorbing electromagneticradiation, in particular solar radiation, according to the preamble ofpatent claim 1.

DE 32 24 688 A1 discloses a solar collector of the type in questionwhich is formed by welded-together sheets of plastic. The sheets ofplastic are divided by weld seams into chambers. These chambers can beflowed through by a heat transfer medium in the form of water. For thispurpose, the chambers are connected in a communicating manner to acommon inlet and a common outlet.

This known device has been successfully used for forming solarcollectors on flat roofs and is particularly distinguished by itslow-cost construction. However, use of such a solar collector on slopingroofs is precluded, since in this case the heat transfer mediumseparates into layers. In the region of the lower chambers especially,this causes pressures that can no longer be withstood by this sheet typeof structure. Consequently, this known solar collector has only amoderate application range. Furthermore, there is the fundamentalproblem that this known solar collector is usually operated in a closedcycle, allowing unfavorable pressure conditions to occur duringoperation even in the case of collectors that are lying flat.

DE 42 37 228 C2 discloses an absorber for solar collectors that isdistinguished by particularly high energy efficiency. For this purpose,the actual absorber is surrounded on the underside and around theperiphery by a heat insulating material. On the upper side, facing thesun, there is a vacuum insulation, which is closed off by a window. Inthis way, good heat insulation is obtained around the absorber, so thatthis absorber can generate high temperatures in the heat transfer mediumeven when the ambient air is cold, such as for example in winter.However, it is not possible for this known solar collector to be formedfrom sheets in accordance with the aforementioned document, since avacuum insulation cannot be obtained with sheets because of the lack ofdimensional stability.

DE 27 20 755 A1 discloses a further solar collector, which has aradiation-absorbent liquid as a heat transfer medium. This measure isintended in particular to prevent problems of overheating during theoperation of the solar collector.

DE 88 10 095 U1 discloses an autonomous solar device for providing hotwater. The device comprises a thin-walled sheet collector which isconnected to a service water line. Since the collector cannot withstandthe pressure in the service water line, a pressure reducer is providedbetween the service water line and the collector. However, this pressurereducer serves exclusively for lowering the pressure in the water line,and consequently cannot limit differences in pressure within thecollector system.

The invention is based on the object of providing a device of the typementioned at the beginning that can be used universally while being of alow-cost construction.

This object is achieved according to the invention by the features ofpatent claim 1.

The device according to claim 1 serves for absorbing electromagneticradiation, in particular solar rays. The main intended use of thisdevice is in the area of solar collectors for the conversion of sunlightinto heat. To make the device inexpensive, it has at least one flexiblesheet pocket, which is divided into chambers. This sheet pocket is inthis case flowed through by a heat transfer medium. The construction inthe form of sheets offers the advantage that the device can betransported very easily. In particular, this device can be rolled orfolded up. Sheets can be produced at very low cost, since they use onlylittle material. The sheets preferably consist of a polymer material,not only pure polymers but also mixed polymers being suitable for use.Polyvinyl chloride, polyethylene and polyurethane have been found to beparticularly successful. To form the sheet pockets, one sheet may befolded over. It is alternatively possible for two sheets to be weldedtogether. Dividing the sheet pocket into chambers allows heat transfermedium to flow uniformly through the sheet pocket and increasedstability of the sheet pocket to be achieved. This is important formaking optimum use of the sunlight. The division may be obtained by weldseams and/or by spaced-apart weld spots. A silicone oil, which remainswell below its boiling point under operating conditions, is preferablyused as the heat transfer medium. In this way, increases in pressurecaused by boiling effects in the heat transfer medium are reliablyavoided. For supplying and discharging the heat transfer medium, thesheet pocket has at least one inlet and at least one outlet. Thesecommunicate with the chambers of the sheet pocket.

If the sheet pockets described are laid on a sloping roof, there is thefundamental problem that different pressures are obtained within thesheet pocket. In particular, owing to gravity, a much greater pressureis obtained in the region of the lower end of the roof than in theregion of the ridge, which leads to considerable pressure loading andstressing of the sheet pocket in the lower region. In principle, thissituation could be counteracted by forming the sheet pocket withcorrespondingly thick walls. However, this measure is contrary to thestated object. Furthermore, in this way the sheet pocket becomesflexurally more rigid, which makes it considerably more difficult tohandle.

To solve this problem, at least one pressure reducer is provided on theinlet side between at least two of the chambers or sheet pockets andreduces the pressure of the heat transfer medium in the chamber. Thismeasure appears to be contrary to the stated object, since the pressurereducers do in fact represent a considerable cost factor. For example, aroof height of 3 m and a maximum pressure of the heat transfer medium of2 kPa would require an arrangement of at least 14 pressure reducers,which makes a significant difference to the cost of the overallinstallation of the solar collector. However, it must be taken intoconsideration in this respect that only one pressure reducer is requiredfor each section over the height of the solar collector, since nogravity-induced pressure differences can build up in a chamber extendinghorizontally over the entire length of the roof.

Furthermore, the pressure reducers can be of a very simple construction,since the aim is essentially for the heat transfer medium to betransported pressurelessly through the device.

In order to prevent pressures from building up between the chambers as aresult of the communicating connection on the outlet side, it isadvantageous according to claim 2 if at least one fluid diode or atleast one pressure reducer is provided on the outlet side between atleast two chambers or sheet pockets. A fluid diode has a low flowresistance in the preferential direction but a great flow resistance inthe opposite direction. This prevents the outlet of a higher-lyingchamber being able to force the heat transfer medium out on the outletside into the chamber lying thereunder. In order to preventcorresponding pressures from being able to build up when the heattransfer medium is stationary, it is enough in this case to provide asufficiently large storage tank, so that the heat transfer medium canalways flow away unhindered. Consequently, the heat transfer medium isonly stationary when the chambers are virtually empty.

This measure at the same time prevents the device from overheating whenthe heat transfer medium is stationary. Alternatively, a pressurereducer may also be provided on the outlet side and reliably exclude thepossibility of excessive pressures occurring. These pressure reducersalso work when the heat transfer medium is stationary.

Claim 3 provides a simple way of creating the pressure reducer, in theform of a section of pipe with foam or fibrous material inserted in it.This material provides the corresponding flow resistance, so that nopressures can build up. The foam or the fibrous material is preferablydimensioned in such a way that it has a capillary effect.

Alternatively or in addition, the pressure reducer may be formed by adrip chamber. This drip chamber interrupts the communicating connectionbetween the individual chambers, so that no pressures can build up fromone chamber to the next.

Alternatively or in addition, the pressure reducer may, according toclaim 5, also be formed by a section of pipe with rungs runningtransversely in relation to the direction of flow. These rungs produce acascade, which likewise has a pressure-reducing effect.

According to claim 6, it is advantageous if the pressure reducer isformed by at least one meander, which likewise has a pressure-reducingeffect by increasing the length of the line.

To achieve a high final temperature of the heat transfer medium, it isimportant to keep heat losses as low as possible. The main heat loss ofa solar collector is formed by the conduction of heat into the ambientair. This heat conduction becomes all the greater the cooler the ambientair is. However, it is particularly when the ambient air is cold thatthe greatest heating power is required. It is therefore expedient tokeep down this loss mechanism. According to claim 7, it is proposed forthis purpose to cover at least the underside of the sheet with at leastone heat insulator. The underside of the sheet has no radiationcoupling-in function and can therefore be thermally insulated in any waydesired. However, the underside of the sheet has a large surface area inrelation to the end faces, and therefore contributes considerably to theheat loss. For this reason, insulation of the underside of the sheet isparticularly effective. Apart from that, it is expedient also toinsulate additionally the end faces of the sheet pocket.

To obtain a further increase in the final temperature of the heattransfer medium, according to claim 8 it is advantageous if the sheetpockets are covered with a heat insulation, at least on the upper side.The insulation of the upper side is particularly expedient because thisside is exposed directly to the ambient air. In addition, winds can alsoblow along the upper side of the sheet pocket and these winds can leadto an increased loss of heat. In order on the other hand not to impairthe radiation absorption too much, however, it is important in the caseof insulation on the upper side to form it from a transparent heatinsulator.

Heat insulating materials that are often used are sensitive to wet andlose a considerable part of their insulating effect in the wet state.For this reason, according to claim 9 it is favorable if the heatinsulator is surrounded by a protective film. This protective filmessentially has the task of keeping wet, especially rain, away from theheat insulation.

To obtain a further improvement in the insulating effect, according toclaim 10 it is favorable if the protective film is gas-filled. This hasthe effect that the protective film lifts off slightly from the heatinsulation, so that the protective film acts like a greenhouse. Inaddition, good protection from hail is obtained in this way.

As a simple way of creating the chambers and the inlet and outlet,according to claim 11 it is advantageous to structure the sheet pocketby means of weld seams. In particular, these weld seams can be producedon a running web of sheet, which makes production particularlyinexpensive.

It is considered in principle to make the side of the sheet pockets thatis facing the radiation source transparent and to color the side facingaway black. This achieves the effect that the electromagnetic radiationpenetrates through the facing sheet and is absorbed by the sheet facingaway. The heat produced in this way in the sheet is then transferred tothe heat transfer medium. According to claim 12, however, it is morefavorable to form the heat transfer medium itself asradiation-absorbent. This also brings into consideration, along with theconfiguration described above of the sheet pockets, an alternative inwhich, for example, both sides of the sheet pocket are transparentlyformed. The use of a radiation-absorbent heat transfer medium means thatthe heat is generated directly in the heat transfer medium, so that heatconduction between the absorber surface and the heat transfer medium isno longer required. In this case, the absorption of the device can alsobe controlled.

If, for example, a circulating pump for the heat transfer medium fails,there is in principle the risk of the heat transfer medium overheating,which could lead to the sheet becoming damaged. If it is provided thatthe heat transfer medium can in this case flow out of the sheet pocketunhindered, the system regulates itself to the extent that, in the eventof failure of the circulating pump, the absorptivity of the device isalso reduced. In this case, the device protects itself from overheating.

In order to shorten the response time of the overheating protection,according to claim 13 it is favorable to use a heat transfer medium withtemperature-dependent radiation absorption. In this case, as thetemperature increases, the absorption of the heat transfer mediumdecreases, possibly abruptly. In the case of imminent overheating of theheat transfer medium, for example if the circulating pump is at astandstill, the radiation absorption is reduced in this way, since theheat transfer medium becomes increasingly more transparent. This,however, also reduces the energy input into the heat transfer medium,which prevents overheating.

According to claim 14, it is favorable to make the sheet pocket or theprotective film UV-resistant or gnaw-proof. Conventional UV stabilizersare used for this. It is additionally considered to incorporate odoroussubstances in the polymer, which deter animals that could bite into thesheet. Examples of such animals are martens and raccoons.

To improve the energy yield, according to claim 15 it is advantageous ifthe sheet pocket or the protective film has at least one photovoltaiccell of semiconducting material. This allows part of the sunlight to beconverted directly into electrical energy, while the portion of thesolar energy that cannot be used for this is converted into heat. Thisportion then serves for heating up the heat transfer medium, to allow itin this way to be put to further use. In this way, a favorablesynergistic effect is obtained, since the heat transfer medium cools thephotovoltaic cells, and consequently also increases their efficiency.

According to claim 16, it is advantageous if at least one valveinfluencing the through-flow of the heat transfer medium or at least onecirculating pump is provided in the supply line or discharge line. It isthereby possible in a simple way to set or control the through-flow rateof the heat transfer medium, in order to obtain an adaptation to ambientconditions. In particular, it is considered to increase the through-flowrate of the heat transfer medium when there is strong solar irradiation,in order in this way to obtain more heat. When there is reduced solarirradiation, on the other hand, the through-flow rate of the heattransfer medium is reduced, in order to ensure a sufficiently hightemperature level. This valve or this circulating pump is preferably inoperative connection with at least one sensor, so that closed-loopcontrol can be achieved in this way. In the simplest case, thetemperature of the heat transfer medium in the outlet line is controlledto a value that still makes it possible for the heat to be used for theplanned purpose. Alternatively, however, more complex closed-loopcontrols are also conceivable, for example controls which optimize theenergy conversion of the overall system. It is also considered to usethe at least one sensor to sense when the collector is covered withsnow, in order to reverse the heat flow of the heat transfer medium. Inthis way, when the collector is covered with snow, the heat transfermedium can introduce heat into the collector, in order to melt the snowthat is on the collector, so that it can subsequently slide off.

Finally, according to claim 17 it is favorable if the device isadhesively fixed on a base. This has the advantage of ruling outmovement of the device in relation to the base that could lead toabrasion caused by scraping effects, and consequently to destruction ofthe device. Furthermore, in this case the device can always be mountedin the same way irrespective of the actual form of the roof. Inparticular, it is not necessary for fastening means to be adapted to theactual form of the roof.

The subject matter of the invention is explained by way of example onthe basis of the drawing, without restricting the scope of protection.

Further advantages and features of the present invention are presentedin the following detailed description on the basis of the associatedfigures, in which a number of exemplary embodiments of the presentinvention are contained. However, it should be understood that thedrawing serves only for the purpose of representing the invention anddoes not restrict the scope of protection of the invention.

In the drawing:

FIG. 1 shows a schematic representation of a house with a solarcollector system,

FIG. 2 shows a three-dimensional view of a device for absorbingelectromagnetic radiation,

FIG. 3 shows a sectional representation through the device according toFIG. 2 along the sectional line III-III,

FIG. 4 shows a schematic representation of a first embodiment of apressure reducer,

FIG. 5 shows a schematic representation of a second embodiment of apressure reducer and

FIG. 6 shows a schematic representation of a third embodiment of apressure reducer.

FIG. 1 shows a schematic representation of a house 1 with a roof 2.Fitted on the roof 2 is a device 3 for absorbing solar radiation, whichis formed by a number of sheet pockets 4. These sheet pockets 4 are inconnection via supply lines 5 and discharge lines 6.

The supply line 5 is in this case in connection with a pressure side ofa circulating pump 7, which pumps a heat transfer medium from a storagetank 8 into the supply line 5. The discharge line 6, on the other hand,is in connection with a heat exchanger 9, which extracts from the heattransfer medium the heat absorbed, in order to make it usable in thehouse 1. From the heat exchanger 9, the heat transfer medium returns tothe storage tank 8.

Installed in the discharge line 6 is a valve 31, which influences thethrough-flow of the heat transfer medium through the discharge line 6.This valve 31 is in operative connection with a controller 34, which isinfluenced by sensors 32, 33. The sensor 32 is in this case a puretemperature sensor, which senses the temperature of the heat transfermedium in the discharge line 6. The sensor 33, on the other hand, is asnow sensor, which may, for example, be formed as a light-sensitivesensor and determines whether the sheet pockets 4 are covered with snow.In addition, the controller 34 influences the circulating pump 7 in thesense of reversing the direction of rotation.

In the simplest case, the controller 34 may effect a temperature controlof the heat transfer medium in the discharge line 6. In this case, theflow of the heat transfer medium is controlled in such a way that aconstant temperature of the heat transfer medium is obtained at thelocation of the temperature sensor 32. Furthermore, the controller 34 isinfluenced by the snow sensor 33, which in the simplest case effects thereversal of the direction of rotation of the circulating pump 7. If snowis covering the sheet pockets 4, in this case the heat transfer mediumis reversed in its direction of flow, so that it does not give off heatin the heat exchanger 9 but is heated up in it. This heat is thenintroduced into the sheet pockets 4, in order to melt the snow lying onthem, and thereby restore the function of the device 3. The snow sensor33 is preferably constructed in such a way that, apart from sensing thethickness of the snow, it also senses snowfall, in order to prevent thesheet pockets 4 from being thawed out the whole time when there iscontinuous snowfall. This provides increased energy efficiency of thedevice 3.

FIGS. 2 and 3 show a three-dimensional view of the sheet pocket 4 withshortened longitudinal extent in relation to FIG. 1. The sheet pocket 4comprises an upper sheet 10 and a lower sheet 11. The two sheets 10, aretransparent, so that sunlight can penetrate through the entire sheetpocket 4 unhindered.

The sheet pocket 4 is provided at the periphery with peripheral weldseams 12, which close the sheet pocket 4 on all sides apart fromopenings 13 for the supply line 5 and the discharge line 6. In order tobe easily able to cascade the sheet pockets 4, the sheet pocket 4 hastwo openings 13 for the supply line 5 and two openings 13 for thedischarge line 6.

The sheet pocket 4 also has separating weld seams 14, which separate thesheet pocket 4 into individual chambers 15. These chambers 15 aredistributed two-dimensionally over virtually the entire sheet pocket 4and are charged via the supply line 5 with a heat transfer medium (notrepresented), which can flow away via the discharge line 6.Consequently, the heat transfer medium, guided by the separating weldseams 14, can essentially only flow through the chambers 15 in thedirection of flow 16.

Pressure reducers (not represented) may be fitted in the supply line 5and discharge line 6 from chamber 15 to chamber 15. In addition, it isalso conceivable to provide a pressure reducer respectively between onlya certain number of chambers 15. It is also considered to arrange apressure reducer respectively between at least two sheet pockets 4 inthe region of the supply line 5 and the discharge line 6. In the regionof the discharge line 6, a simple fluid diode may be used instead of apressure reducer.

To reduce the losses from heat conduction with the surrounding air, thesheet pocket 4 is surrounded on all sides by a heat insulator 17. Thisheat insulator 17 is transparent, at least on the upper side, in orderto keep reflection of the incident electromagnetic radiation as small aspossible. On the underside of the sheet pocket 4, any desired heatinsulator 17 may be used.

In order to prevent the heat insulator 17 from becoming soaked through,and consequently being restricted in its insulating capability, theentire arrangement is encased in a protective film 18, which in turn isperipherally sealed off by weld seams 19. Distributed in these weldseams 19 are eyelets 20, which allow simple fastening of the sheetpocket 4 to the roof 2 of the house 1 by lashing. Alternatively or inaddition, the sheet pocket 4 may also be adhesively attached to the roof2. On at least one longitudinal side, the sheet pocket 4 is drawn outuntil it overlaps with the weld seam 19 and is provided with flusheyelets 20. In this way, the sheet pocket 4 is kept in position withinthe protective film 18. The drawn-out periphery is preferably located atthe higher longitudinal edge.

FIG. 4 shows a schematic representation of a first embodiment of apressure reducer 21. The supply line 5 is in connection with a branchline 22, which is led directly into a chamber 15. The supply line 5 isclosed at the end by a plate 23, in order to prevent an increasingpressure from building up from chamber 15 to chamber 15 owing togravity.

Arranged in the supply line 5 is a valve 24, which sits on a membrane25. The membrane 25 is loaded from the outside with air pressure of theambient air and in this way forms a pressure sensor. On the left side,the membrane 25 is acted upon by the heat transfer medium, so that thevalve 24 closes whenever the pressure of the heat transfer medium in amembrane chamber 26 exceeds a specific value. In this way, a definedfluid pressure is obtained in the membrane chamber 26. The membranechamber 26 is in connection via an opening 27 with the supply line 5 ofthe following pressure reducer 21.

FIG. 5 shows an alternative embodiment of a pressure reducer 21. In thecase of this embodiment, a supply line 5 with increased cross section isused. Inside the pressure line 5 there is a foam or fibrous material 28,which has capillary effects. This capillary effect excludes thepossibility of gravity-induced pressures building up via the supply line5.

Finally, FIG. 6 shows a further alternative embodiment of a pressurereducer 21. In this case, the supply line 5 has a cross-sectionalnarrowing 29 at its free end. This cross-sectional narrowing 29 providesa drip system, through which a drip chamber 30 is filled with the heattransfer medium. On account of the drop in height caused by the dripsystem, the individual branch lines 22 are no longer connected in acommunicating manner by the heat transfer medium.

Since some exemplary embodiments of the present invention are not shownor described, it should be understood that many changes andmodifications to these described exemplary embodiments are possible,without departing from the essential concept and protective scope of theinvention that is established by the claims.

LIST OF DESIGNATIONS

-   1 House-   2 Roof-   3 Device-   4 Sheet pocket-   5 Supply line-   6 Discharge line-   7 Circulating pump-   8 Storage tank-   9 Heat exchanger-   10 Upper sheet-   11 Lower sheet-   12 Peripheral weld seam-   13 Opening-   14 Separating weld seam-   15 Chamber-   16 Direction of flow-   17 Heat insulator-   18 Protective film-   19 Weld seam-   20 Eyelet-   21 Pressure reducer-   22 Branch line-   23 Plate-   24 Valve-   25 Membrane-   26 Membrane chamber-   27 Opening-   28 Foam or fibrous part-   29 Cross-sectional narrowing-   30 Drip chamber-   31 Valve-   32 Temperature sensor-   33 Snow sensor-   34 Controller

1. A device for absorbing electromagnetic radiation, in particular solarradiation, the device (3) having at least one flexible sheet pocket (4),which is divided into chambers (15), which are connected to at least onesupply line (5) for introducing a heat transfer medium and at least onedischarge line (6) for letting out the heat transfer medium,characterized in that the device (3) has on the inlet side between atleast two of the chambers (15) and/or sheet pockets (4) at least onepressure reducer (21), which limits the pressure of the heat transfermedium.
 2. The device as claimed in claim 1, characterized in that atleast one fluid diode and/or at least one pressure reducer (21) isprovided on the outlet side between at least two of the chambers (15)and/or sheet pockets (4).
 3. The device as claimed in claim 1 or 2,characterized in that the pressure reducer (21) is formed by a sectionof pipe into which a foam and/or fibrous material (28) has beeninserted.
 4. The device as claimed in claim 1 or 2, characterized inthat the pressure reducer (21) is formed by a drip chamber (30).
 5. Thedevice as claimed in claim 1 or 2, characterized in that the pressurereducer (21) is formed by a section of pipe with rungs runningtransversely in relation to the direction of flow.
 6. The device asclaimed in claim 1 or 2, characterized in that the pressure reducer (21)is formed by a meander.
 7. The device as claimed in at least one ofclaims 1 to 6, characterized in that the sheet pocket (4) is coveredwith at least one heat insulator (17), at least on the underside.
 8. Thedevice as claimed in at least one of claims 1 to 7, characterized inthat the sheet pocket (4) is covered with at least one transparent heatinsulator (7), at least on the upper side.
 9. The device as claimed inclaim 7 or 8, characterized in that the heat insulator (17) issurrounded by a protective film (9).
 10. The device as claimed in claim9, characterized in that the protective film (18) is gas-filled.
 11. Thedevice as claimed in at least one of claims 1 to 10, characterized inthat the sheet pocket (4) is divided into chambers (15) and/or sectionsof pipe by separating weld seams (14).
 12. The device as claimed in atleast one of claims 1 to 11, characterized in that the heat transfermedium is radiation-absorbent.
 13. The device as claimed in claim 12,characterized in that the heat transfer medium has atemperature-dependent radiation absorption, the absorption of whichdecreases with increasing temperature.
 14. The device as claimed in atleast one of claims 1 to 13, characterized in that the sheet pocket (4)and/or the protective film (18) is made UV-resistant and/or gnaw-proof.15. The device as claimed in at least one of claims 1 to 14,characterized in that the sheet pocket (4) and/or the protective film(18) has at least one photovoltaic cell of semiconducting material. 16.The device as claimed in at least one of claims 1 to 15, characterizedin that, to influence the through-flow of the heat transfer medium, atleast one valve and/or at least one circulating pump is provided in thesupply line (5) and/or discharge line (6) and is preferably in operativeconnection with at least one sensor (32, 33).
 17. The device as claimedin at least one of claims 1 to 16, characterized in that the device (3)is adhesively fixed on a base (2).